There are generally two types of projection screens used today. The first, and most common, is a front projection screen wherein the image is cast onto the screen from the same direction in which the image is viewed by an audience. The second type is a rear projection screen wherein the image is cast from the opposite, or rear, side of the screen relative to the location of the audience. In some applications of rear projection screens, more than one panel may be used to display several images or to display one large image as materials commonly used in the industry prohibit the manufacture of a sufficiently large single screen. In installations where multi-panel construction is desired, a framing system needs to be provided that connects adjacent screens without significantly reducing the viewing surface of each screen, minimizes the gaps between adjacent screens, prevents an image for one screen from overlapping onto an adjacent screen, and allows coplanar and angular orientations of adjacent screens. It is also desirable for such a framing system to be inexpensive, easy to install, easy to maintain, and capable of accommodating rear projection screens of various thicknesses and sizes.
Pre-formed frame assemblies are disclosed in U.S. Pat. Nos. 4,895,429, and 4,984,871. Such assemblies are used to join adjacent panels, or screens, of a particular size and at a specific angle with respect to each other. Frame assemblies in which each screen edge is placed in a U-shaped channel are difficult to install and to maintain. The frame can not be completely assembled before screens are placed in the frame, because, for each screen, the fourth U channel can be put into place only after the screen has been inserted in the first three U channels. Also, replacing a single screen in the middle of the multi-panel matrix requires that the side screens be first removed in order to gain access to the middle screen.
Other connectors, such as those disclosed in U.S. Pat. No. 4,895,429, require that fasteners, screws or bolts, be inserted through holes in the screens. Although these connectors are capable of accommodating a light-blocking fin to prevent the image intended to be displayed on one screen from being displayed on an adjacent screen, they do not allow for non-coplanar orientations of the front surfaces of the adjacent screens. They also require that dual fasteners, one through each screen, be utilized. The screen holes needed to accommodate the fasteners reduce the structural strength of the screen. Specifically, to avoid reducing the viewing surface of the screen, the holes required for the fasteners are made close to the edge of the screen which may weaken the edge and which may result in damage to the edge of the screen during assembly.
U.S. Pat. No. 4,668,046 discloses two other types of connectors used to join adjacent screens. One connector is limited to vertically join adjacent screens without a horizontal framing member above or below the vertically joined screens. A second connector includes holder plates secured to the ends of the screens and to a fin, which are, in turn, fastened to each other. This connector requires that a fin be utilized and also weakens the ends of the screens by the placement of many fasteners through the holder plates into the ends of the screen.
Other fasteners are disclosed in U.S. Pat. Nos. 3,841,045, 4,254,600 and 4,917,528.